Vacuum pump

ABSTRACT

A vacuum pump includes a housing, a rotor located in the housing and having a shaft and pump-active elements supported on the shaft, a stator having pump-active elements and located in a separate housing part of the housing, for driving the pump, bearings for rotatably supporting the rotor shaft, and at least one vacuum chamber located in the housing.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a vacuum pump including a housing, arotor located in the housing and having a shaft and pump-active elementssupported on the shaft, a stator located in the housing and havingpump-active elements, with the housing having a housing part for holdingthe pump-active elements of the stator, drive means for driving the pumpand bearing means for rotatably supporting the rotor shaft.

2. Description of the Prior Art

Vacuum pumps form, together with vacuum chambers, vacuum systems withwhich numerous tasks can be performed. These tasks range frommanufacturing monolithic layers through analyses of gases, and up tooptical columns of high-resolution electronic microscopes. The technicaldevelopments put higher and higher requirements to the vacuum tightnessand compactness of the vacuum systems.

In some common applications, so-called differential pumps are used. Withdifferential pumps, a system is formed of vacuum pumps connected witheach other, with separate vacuum chambers being held at different gaspressures.

A noticeable simplification of formation of a pump system fordifferential pumps is disclosed in German Patent DE-PS 43 31 589.Instead of a plurality of pumps, a single vacuum pump takes overevacuation of vacuum chambers.

European Patent EP-PS 1 090 231 discloses a vacuum pump with a doublehousing. An inner housing combines a rotor/stator region and adrive/bearing region of the pump. The inner housing is then pushed intoan outer housing that is adapted to a particular use. However, thelatter solution has serious drawbacks, a double housing is expensive asmore parts are used than with a single-part housing. This increases bothexpenses associated with manufacturing of the housing components andexpenses associated with the assembly of numerous components. Thecontact surfaces of the two housings must be machined with a highprecision. The danger of a virtual leak increases with an increase ofnumber of components needed for the housing. Between the two separatehousings, seals must be provided which, because of their large number,increase the risk of leakage. For a double housing, additional spaceshould be provided, which makes gas feeding more expensive. Theseproblems are independent of the number of vacuum chambers provided inthe vacuum system.

Accordingly, an object of the invention is a vacuum pump in which theproblems, which are associated with a double housing, are eliminated.

Another object of the invention is a vacuum pump having a compactconstruction and requiring a small number of parts.

SUMMARY OF THE INVENTION

These and other objects of the present invention, which will becomeapparent hereinafter, are achieved by providing a vacuum pump in whichthe housing part which serves for holding pump-active stator elements,has at least one vacuum chamber. This noticeably reduces the number ofnecessary parts. A smaller number of flanges and other housingtransition elements becomes necessary, whereby vacuum tightnessincreases and expenses decreases. Generally, a very compact unit isprovided. Because a flange connection between the vacuum chamber andvacuum pump, which is necessary in the existing state of the art, iseliminated, the vacuum tightness is noticeably increased. This permitsto achieve lower end pressures with the inventive vacuum pump.

A further reduction of the number of parts is achieved when the separatehousing part further holds at least one component of bearing and drivemeans.

According to the invention, the inventive vacuum pump has a plurality ofpumping stages with each of which a vacuum chamber is connected, withthe vacuum chambers being also connected with each other. Thereby, asingle component, such as a housing, is necessary for all chambers inthe vacuum pump, which reduces costs and increases tightness. With thegas pressure in the respective chambers being different, a plurality ofdifferential pumps are provided in the vacuum pump.

According to the invention the bearing means includes a permanent magnetbearing for supporting an end of the rotor shaft. This bearing does notrequire lubrication and is wear-free and, thus, can be used in thehigh-vacuum region of a vacuum pump.

According to a further modification of the present invention, forproduction of the high vacuum, the pump-active rotor elements and thepump-active stator elements includes blades forming at least onehigh-vacuum pumping stage. This is particularly suitable for obtaininglow pressures.

According to a further development of the present invention, the atleast one vacuum chamber has an opening, and the vacuum pump furtherincludes a releasable cover for closing the opening, and at least twoseals for sealing the opening. The opening provides for an easy accessto the vacuum chamber so that, e.g., maintenance becomes possible, orthe components located in the vacuum chamber, e.g., of some experiment,can be very easily replaced. The opening-sealing seals insure the vacuumtightness.

The arrangement discussed above can be further improved by providing anannular channel between the two seals and in which vacuum is produced.Thereby, the pressure drop between the atmospheric pressure and vacuumtakes place in stages, which reduces forces acting on the seals. Becausethe leakage rate of a leak depends on the pressure difference betweenthe inner and outer sides, and the stagewise pressure drops means asmaller pressure difference across a seal, smaller leaks play a smallerrole. By measuring the power consumption of a pump used for producingvacuum, leakage at the seals can be determined.

According to further development of the present invention, there isprovided a push-in or insertable module in which at least one of thevacuum chambers is located. The insertable module is pushed in a boreformed in the vacuum pump housing and is retained there. Thereby, it ispossible to replace the vacuum chamber system of the inventive vacuumpump and adapt it to other requirements. In addition, it is possible tohave the vacuum chambers and the vacuum pump produced by differentmanufactures. This reduces costs because manufacturing steps take placeparallel with each other and respective professional skills andknowledge are optimally used.

According to a further advantageous embodiment of the present invention,for producing vacuum in the annular channel, there is provided aconnection conduit integrated in the housing between the annular channeland one of pumping stages and gas outlet channel.

The novel features of the present invention, which are considered ascharacteristic for the invention, are set forth in the appended claims.The invention itself, however, both as to its construction and its modeof operation, together with additional advantages and objects thereof,will be best understood from the following detailed description ofpreferred embodiments, when read with reference to the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings show:

FIG. 1 a cross-sectional view of a first embodiment of a vacuum pumpaccording to the present invention;

FIG. 2 a cross-sectional view of a second embodiment of a vacuum pumpaccording to the present invention; and

FIG. 3 a cross-sectional view of a third embodiment of a vacuum pumpaccording to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A vacuum pump 1 according to the present invention, a first embodimentof which is shown in FIG. 1, has a housing 2 and a lower housing part 3.A shaft 4 is supported at one of its ends by bearing means 8 and at itsanother opposite end by a permanent magnetic bearing 17. The permanentmagnetic bearing 17 is located at a high-vacuum side of the pump systemand is secured thereat by a support structure 16. The pump systemincludes pump-active rotor elements 5 supported on the shaft 4, andstationary pump-active stator elements 6. In the embodiment shown in thedrawings, rotor and stator elements are formed as blade-carrying discs,whereby a vacuum pump in accordance with a known constructionalprinciple of turbomolecular pumps is formed. However, the presentinvention is not limited to this type of a vacuum pump, rather it isapplicable to a combination of different types in accordance with apressure region that should be obtained. E.g., the invention isapplicable to Holweck stages and the like. The stator has, in additionto pump-active elements 6, spacers 7 which determine the axial distanceof the stator elements from each other. The stator components are firstinserted through the housing 2 of the vacuum pump 1, mounted in theirrespective positions and are held there. Without the housing 2, thismounting is not given, the remaining pump part is not itselfoperational.

In the housing part 3, in addition to bearing means 8, there is provideddrive means 9, e.g., electrical coils which cooperate with permanentmagnets arranged on the shaft 4, setting the shaft in rapid rotation.The bearing means 8 can be formed as a ball bearing, magnetic bearing,or gas bearing. The lower housing part 3 also includes a gas outletchannel 30 leading to a gas outlet union. When the vacuum pump itself isnot compressed to the atmospheric pressure, a forevacuum pump isconnected with this gas outlet union.

Also are arranged in the housing 2, a first vacuum chamber 20 and asecond vacuum chamber 21, with a lower pressure being produced in thefirst vacuum chamber 20 than in the second vacuum chamber 21.

The first vacuum chamber 20 is directly connected with the first pumpingstage 22 of the pump system. The second vacuum chamber 21 is connectedby a suction channel 10 with an intermediate inlet 18. Through theintermediate inlet 18, gas can be fed to the second pumping stage 23.Thus, gas from the first vacuum chamber 20 is fed into both the firstpumping stage 22 and the second pumping stage 23 and is compressedthere, whereas gas from the second vacuum chamber 21 is compressed onlyin the second pumping stage 23. This principle can be expanded furtherby providing further vacuum chambers in the housing 2. The furthervacuum chambers can be connected with further intermediate inlets of thepump system. Likewise, one of the chambers can be connected with the gasoutlet channel 30 by a channel formed in the housing. The first andsecond vacuum chambers 20 and 21 are connected with each other by aconnection passage 25. The passage 25 can be formed as a bore in thehousing 2 or as a throttle. The second vacuum chamber 21 has an opening26 through which, e.g., a to-be-analyzed gas or a particle stream canflow in.

The housing 2 has an opening that can be closed by a cover 11 and whichis connected with the first vacuum chamber. The cover 11 permits tomonitor components which are located in the first vacuum chamber 20.Around this opening, two seals are provided, with a first seal 12surrounding the opening and the second seal 13 surrounding the firstseal 12. An annular channel 14 is provided between the seals 12 and 13and in which vacuum is produced. For producing the vacuum, there isprovided a connection conduit 15 that opens either in one of the pumpingstages of the vacuum pump or in the gas outlet channel 30. When theconnection conduit opens not in front of the first pumping stage but atthe other location of the pump system, the vacuum, which is producedbetween the two seals 12 and 13, is between the pressure in the firstvacuum chamber 20 and the pressure of the vacuum pump environment.Thereby, the load, which act on separate seals, is noticeably reduced asthe pressure drop across a respective seal is smaller. Measurement ofdrive power of the pump or the pumping stage necessary for producing thevacuum permits to make a conclusion about leakage and whether the sealsare defective.

The vacuum pump according to the first embodiment has a furtheradvantage achieved with the present invention, namely, when all ofvacuum conduits between the chambers, chambers and pumping stages, andto the annular channel in the housing are integrated, only oneforevacuum flange is necessary. Additional expensive conduits, whichshould be attached later, are eliminated.

In the vacuum pump according to a second embodiment, which is shown inFIG. 2, the invention is applied to a three-chamber system. There areprovided in the housing 2 of the vacuum pump a first chamber 31 in whicha high vacuum is produced, a second chamber 32 in which a medium vacuumis produced, and a third chamber 33. The third vacuum chamber 33 isretained at a forevacuum level. The third vacuum chamber 33 is connectedvia a forevacuum inlet 37 with the gas outlet channel 30 of the vacuumpump. A middle inlet 36 connects the second vacuum chamber 32 with thepumping system of the vacuum pump. A high vacuum inlet 35 connects thefirst vacuum chamber 31 with the pump system. Gas, which reaches thepump system through the high vacuum inlet 35 should flow over all of theparts of the pump system. The stationary components, stator discs 6 andspacers 7 should only be mounted in the housing 2 and retained in theirpositions. Without the housing 2, this mounting of stationary componentsis not possible, and remaining pump components themselves are notoperational. As a rule, it is necessary to optimize conductance betweenthe chambers and the respective parts of the pump system. A parameterwhich permits to achieve optimization, is angle α between the rotor axis40 and the chamber axis 41. This parameter can vary between 0°, i.e.,with parallel arrangement, and 90°, i.e., with a mutually perpendiculararrangement.

A third embodiment of a vacuum pump according to the present inventionis shown in FIG. 3. The third embodiment differs from the secondembodiment by the vacuum chambers. At least one of the vacuum chambers,here, two vacuum chambers 32 and 33 are arranged in an insertable module44. This module 44 is inserted through a bore formed in the housing 2 ofthe vacuum pump 1 and is secured in the housing 2. To provide forservicing or exchange of the module, the module 44 can be releasablysecured, e.g., with screws. Seals 45 seal the module 44 against thehousing 2. The vacuum chambers 32, 33 are connected with each other asthe chambers 32 and 31 that is formed in the housing 2. All or, as shownin FIG. 3, only some of the chambers can be provided in the insertablemodule. Suction channels 42, 43 connect the vacuum chambers 32, 33 withdifferent parts of the pump system of the vacuum pump, so that differentpressure can be produced in the vacuum chambers.

Though the present invention was shown and described with references tothe preferred embodiments, such are merely illustrative of the presentinvention and are not to be construed as a limitation thereof andvarious modifications of the present invention will be apparent to thoseskilled in the art. It is therefore not intended that the presentinvention be limited to the disclosed embodiments or details thereof,and the present invention includes all variations and/or alternativeembodiments within the spirit and scope of the present invention asdefined by the appended claims.

1. A vacuum pump, comprising a housing; a rotor located in the housingand having a shaft and pump-active elements supported on the shaft; astator located in the housing and having pump-active elements, thehousing having a housing part for holding the pump-active elements ofthe stator; drive means for driving the pump; bearing means forrotatably supporting the rotor shaft; and at least one vacuum chamberlocated in the housing part.
 2. A vacuum pump, according to claim 1,wherein the housing part contains at least one part of the bearing meansand drive means and connectable with the housing.
 3. A vacuum pumpaccording to claim 1, comprising at least two pumping stages, and atleast one further vacuum chamber located in the housing, and wherein theat least one and the further vacuum chambers are connected with eachother and with a respective pumping stage.
 4. A vacuum pump according toclaim 3, wherein the gas pressure in the at least one and further vacuumchambers is not the same.
 5. A vacuum pump according to claim 1, whereinthe bearing means comprises a permanent magnet bearing for supporting anend of the rotor shaft.
 6. A vacuum pump according to claim 3, whereinthe pump-active rotor elements and the pump-active stator elementsincludes blades forming at least one pumping stage.
 7. A vacuum pumpaccording to claim 1, wherein the at least one vacuum chamber has anopening, the vacuum pump further comprising a releasable cover forclosing the opening, and at least two seals for sealing the opening. 8.A vacuum pump according to claim 7, comprising an annular channelarranged between the two seals and in which vacuum is produced.
 9. Avacuum pump according to claim 8, comprising a connection conduitintegrated in the housing between the annular channel and one of pumpingstage and gas outlet channel.
 10. A vacuum pump according to claim 1,further comprising at least one further vacuum chamber, at least one ofthe at least one and further vacuum chambers being located in aninsertable module.